Field of the Disclosure
The present disclosure relates to an organic light emitting diode, and more particularly, to a display device including an organic light emitting diode with improved light extraction efficiency.
Description of the Related Art
An organic light emitting diode display device is a self-light emitting display device and, unlike a liquid crystal display device, does not need a separate light source. Thus, the organic light emitting diode display device can be lightweight and have a compact size. Further, the organic light emitting diode display device is driven at a low voltage, which reduces power consumption, which is an advantageous feature of the organic light emitting diode display device. Also, the organic light emitting diode display device has excellent color expression ability, a high response speed, a wide viewing angle, and a high contrast ratio (CR). Therefore, the organic light emitting diode display device has been researched as a next-generation display device.
Light emitted from an organic emission layer of the organic light emitting diode generally passes through various elements in the organic light emitting diode display device to the outside. However, a part of the light emitted from the organic emission layer may not be transmitted to the outside of the organic light emitting diode display device but may be confined within the organic light emitting diode display device, which reduces the light extraction efficiency of the organic light emitting diode display device.
For example, in a bottom-emission organic light emitting diode display device, about 50% of the light emitted form an organic emission layer is confined within the organic light emitting diode display device due to total reflection or light absorption at an anode electrode, and about 30% of the light emitted from the organic emission layer is confined within the organic light emitting diode display device due to total reflection or light absorption at a substrate.
As such, about 80% of the light emitted from the organic emission layer is confined within the organic light emitting diode display device and only about 20% of the light is transmitted to the outside. Thus, the organic light emitting diode display device has low luminous efficiency.
In order to improve the light extraction efficiency of the organic light emitting diode display device, a method of forming a micro lens array (MLA) on an overcoating layer of the organic light emitting diode display device has been developed. However, even if the micro lens array is formed on the overcoating layer of the organic light emitting diode display device, a large amount of light is confined within the device, and only a small amount of light is transmitted to the outside.
Further, because the micro lens array is formed on the overcoating layer, emission areas of the organic light emitting diode display device may differ in luminous efficiency. Thus, a bright image may be formed in an area with a high luminous efficiency, and a dark image maybe formed in an area with a low luminous efficiency.
Accordingly, there has been a demand for an organic light emitting diode display device that can improve luminous efficiency.